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Linux/mm/mremap.c

  1 /*
  2  *      mm/mremap.c
  3  *
  4  *      (C) Copyright 1996 Linus Torvalds
  5  *
  6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
  7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  8  */
  9 
 10 #include <linux/mm.h>
 11 #include <linux/hugetlb.h>
 12 #include <linux/shm.h>
 13 #include <linux/ksm.h>
 14 #include <linux/mman.h>
 15 #include <linux/swap.h>
 16 #include <linux/capability.h>
 17 #include <linux/fs.h>
 18 #include <linux/swapops.h>
 19 #include <linux/highmem.h>
 20 #include <linux/security.h>
 21 #include <linux/syscalls.h>
 22 #include <linux/mmu_notifier.h>
 23 #include <linux/sched/sysctl.h>
 24 #include <linux/uaccess.h>
 25 #include <linux/mm-arch-hooks.h>
 26 
 27 #include <asm/cacheflush.h>
 28 #include <asm/tlbflush.h>
 29 
 30 #include "internal.h"
 31 
 32 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 33 {
 34         pgd_t *pgd;
 35         pud_t *pud;
 36         pmd_t *pmd;
 37 
 38         pgd = pgd_offset(mm, addr);
 39         if (pgd_none_or_clear_bad(pgd))
 40                 return NULL;
 41 
 42         pud = pud_offset(pgd, addr);
 43         if (pud_none_or_clear_bad(pud))
 44                 return NULL;
 45 
 46         pmd = pmd_offset(pud, addr);
 47         if (pmd_none(*pmd))
 48                 return NULL;
 49 
 50         return pmd;
 51 }
 52 
 53 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 54                             unsigned long addr)
 55 {
 56         pgd_t *pgd;
 57         pud_t *pud;
 58         pmd_t *pmd;
 59 
 60         pgd = pgd_offset(mm, addr);
 61         pud = pud_alloc(mm, pgd, addr);
 62         if (!pud)
 63                 return NULL;
 64 
 65         pmd = pmd_alloc(mm, pud, addr);
 66         if (!pmd)
 67                 return NULL;
 68 
 69         VM_BUG_ON(pmd_trans_huge(*pmd));
 70 
 71         return pmd;
 72 }
 73 
 74 static pte_t move_soft_dirty_pte(pte_t pte)
 75 {
 76         /*
 77          * Set soft dirty bit so we can notice
 78          * in userspace the ptes were moved.
 79          */
 80 #ifdef CONFIG_MEM_SOFT_DIRTY
 81         if (pte_present(pte))
 82                 pte = pte_mksoft_dirty(pte);
 83         else if (is_swap_pte(pte))
 84                 pte = pte_swp_mksoft_dirty(pte);
 85 #endif
 86         return pte;
 87 }
 88 
 89 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 90                 unsigned long old_addr, unsigned long old_end,
 91                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
 92                 unsigned long new_addr, bool need_rmap_locks)
 93 {
 94         struct address_space *mapping = NULL;
 95         struct anon_vma *anon_vma = NULL;
 96         struct mm_struct *mm = vma->vm_mm;
 97         pte_t *old_pte, *new_pte, pte;
 98         spinlock_t *old_ptl, *new_ptl;
 99 
100         /*
101          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
102          * locks to ensure that rmap will always observe either the old or the
103          * new ptes. This is the easiest way to avoid races with
104          * truncate_pagecache(), page migration, etc...
105          *
106          * When need_rmap_locks is false, we use other ways to avoid
107          * such races:
108          *
109          * - During exec() shift_arg_pages(), we use a specially tagged vma
110          *   which rmap call sites look for using is_vma_temporary_stack().
111          *
112          * - During mremap(), new_vma is often known to be placed after vma
113          *   in rmap traversal order. This ensures rmap will always observe
114          *   either the old pte, or the new pte, or both (the page table locks
115          *   serialize access to individual ptes, but only rmap traversal
116          *   order guarantees that we won't miss both the old and new ptes).
117          */
118         if (need_rmap_locks) {
119                 if (vma->vm_file) {
120                         mapping = vma->vm_file->f_mapping;
121                         i_mmap_lock_write(mapping);
122                 }
123                 if (vma->anon_vma) {
124                         anon_vma = vma->anon_vma;
125                         anon_vma_lock_write(anon_vma);
126                 }
127         }
128 
129         /*
130          * We don't have to worry about the ordering of src and dst
131          * pte locks because exclusive mmap_sem prevents deadlock.
132          */
133         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
134         new_pte = pte_offset_map(new_pmd, new_addr);
135         new_ptl = pte_lockptr(mm, new_pmd);
136         if (new_ptl != old_ptl)
137                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
138         arch_enter_lazy_mmu_mode();
139 
140         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
141                                    new_pte++, new_addr += PAGE_SIZE) {
142                 if (pte_none(*old_pte))
143                         continue;
144                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
145                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
146                 pte = move_soft_dirty_pte(pte);
147                 set_pte_at(mm, new_addr, new_pte, pte);
148         }
149 
150         arch_leave_lazy_mmu_mode();
151         if (new_ptl != old_ptl)
152                 spin_unlock(new_ptl);
153         pte_unmap(new_pte - 1);
154         pte_unmap_unlock(old_pte - 1, old_ptl);
155         if (anon_vma)
156                 anon_vma_unlock_write(anon_vma);
157         if (mapping)
158                 i_mmap_unlock_write(mapping);
159 }
160 
161 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
162 
163 unsigned long move_page_tables(struct vm_area_struct *vma,
164                 unsigned long old_addr, struct vm_area_struct *new_vma,
165                 unsigned long new_addr, unsigned long len,
166                 bool need_rmap_locks)
167 {
168         unsigned long extent, next, old_end;
169         pmd_t *old_pmd, *new_pmd;
170         bool need_flush = false;
171         unsigned long mmun_start;       /* For mmu_notifiers */
172         unsigned long mmun_end;         /* For mmu_notifiers */
173 
174         old_end = old_addr + len;
175         flush_cache_range(vma, old_addr, old_end);
176 
177         mmun_start = old_addr;
178         mmun_end   = old_end;
179         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
180 
181         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
182                 cond_resched();
183                 next = (old_addr + PMD_SIZE) & PMD_MASK;
184                 /* even if next overflowed, extent below will be ok */
185                 extent = next - old_addr;
186                 if (extent > old_end - old_addr)
187                         extent = old_end - old_addr;
188                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
189                 if (!old_pmd)
190                         continue;
191                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
192                 if (!new_pmd)
193                         break;
194                 if (pmd_trans_huge(*old_pmd)) {
195                         if (extent == HPAGE_PMD_SIZE) {
196                                 bool moved;
197                                 VM_BUG_ON_VMA(vma->vm_file || !vma->anon_vma,
198                                               vma);
199                                 /* See comment in move_ptes() */
200                                 if (need_rmap_locks)
201                                         anon_vma_lock_write(vma->anon_vma);
202                                 moved = move_huge_pmd(vma, new_vma, old_addr,
203                                                     new_addr, old_end,
204                                                     old_pmd, new_pmd);
205                                 if (need_rmap_locks)
206                                         anon_vma_unlock_write(vma->anon_vma);
207                                 if (moved) {
208                                         need_flush = true;
209                                         continue;
210                                 }
211                         }
212                         split_huge_pmd(vma, old_pmd, old_addr);
213                         if (pmd_none(*old_pmd))
214                                 continue;
215                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
216                 }
217                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
218                                                       new_pmd, new_addr))
219                         break;
220                 next = (new_addr + PMD_SIZE) & PMD_MASK;
221                 if (extent > next - new_addr)
222                         extent = next - new_addr;
223                 if (extent > LATENCY_LIMIT)
224                         extent = LATENCY_LIMIT;
225                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
226                           new_vma, new_pmd, new_addr, need_rmap_locks);
227                 need_flush = true;
228         }
229         if (likely(need_flush))
230                 flush_tlb_range(vma, old_end-len, old_addr);
231 
232         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
233 
234         return len + old_addr - old_end;        /* how much done */
235 }
236 
237 static unsigned long move_vma(struct vm_area_struct *vma,
238                 unsigned long old_addr, unsigned long old_len,
239                 unsigned long new_len, unsigned long new_addr, bool *locked)
240 {
241         struct mm_struct *mm = vma->vm_mm;
242         struct vm_area_struct *new_vma;
243         unsigned long vm_flags = vma->vm_flags;
244         unsigned long new_pgoff;
245         unsigned long moved_len;
246         unsigned long excess = 0;
247         unsigned long hiwater_vm;
248         int split = 0;
249         int err;
250         bool need_rmap_locks;
251 
252         /*
253          * We'd prefer to avoid failure later on in do_munmap:
254          * which may split one vma into three before unmapping.
255          */
256         if (mm->map_count >= sysctl_max_map_count - 3)
257                 return -ENOMEM;
258 
259         /*
260          * Advise KSM to break any KSM pages in the area to be moved:
261          * it would be confusing if they were to turn up at the new
262          * location, where they happen to coincide with different KSM
263          * pages recently unmapped.  But leave vma->vm_flags as it was,
264          * so KSM can come around to merge on vma and new_vma afterwards.
265          */
266         err = ksm_madvise(vma, old_addr, old_addr + old_len,
267                                                 MADV_UNMERGEABLE, &vm_flags);
268         if (err)
269                 return err;
270 
271         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
272         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
273                            &need_rmap_locks);
274         if (!new_vma)
275                 return -ENOMEM;
276 
277         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
278                                      need_rmap_locks);
279         if (moved_len < old_len) {
280                 err = -ENOMEM;
281         } else if (vma->vm_ops && vma->vm_ops->mremap) {
282                 err = vma->vm_ops->mremap(new_vma);
283         }
284 
285         if (unlikely(err)) {
286                 /*
287                  * On error, move entries back from new area to old,
288                  * which will succeed since page tables still there,
289                  * and then proceed to unmap new area instead of old.
290                  */
291                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
292                                  true);
293                 vma = new_vma;
294                 old_len = new_len;
295                 old_addr = new_addr;
296                 new_addr = err;
297         } else {
298                 arch_remap(mm, old_addr, old_addr + old_len,
299                            new_addr, new_addr + new_len);
300         }
301 
302         /* Conceal VM_ACCOUNT so old reservation is not undone */
303         if (vm_flags & VM_ACCOUNT) {
304                 vma->vm_flags &= ~VM_ACCOUNT;
305                 excess = vma->vm_end - vma->vm_start - old_len;
306                 if (old_addr > vma->vm_start &&
307                     old_addr + old_len < vma->vm_end)
308                         split = 1;
309         }
310 
311         /*
312          * If we failed to move page tables we still do total_vm increment
313          * since do_munmap() will decrement it by old_len == new_len.
314          *
315          * Since total_vm is about to be raised artificially high for a
316          * moment, we need to restore high watermark afterwards: if stats
317          * are taken meanwhile, total_vm and hiwater_vm appear too high.
318          * If this were a serious issue, we'd add a flag to do_munmap().
319          */
320         hiwater_vm = mm->hiwater_vm;
321         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
322 
323         /* Tell pfnmap has moved from this vma */
324         if (unlikely(vma->vm_flags & VM_PFNMAP))
325                 untrack_pfn_moved(vma);
326 
327         if (do_munmap(mm, old_addr, old_len) < 0) {
328                 /* OOM: unable to split vma, just get accounts right */
329                 vm_unacct_memory(excess >> PAGE_SHIFT);
330                 excess = 0;
331         }
332         mm->hiwater_vm = hiwater_vm;
333 
334         /* Restore VM_ACCOUNT if one or two pieces of vma left */
335         if (excess) {
336                 vma->vm_flags |= VM_ACCOUNT;
337                 if (split)
338                         vma->vm_next->vm_flags |= VM_ACCOUNT;
339         }
340 
341         if (vm_flags & VM_LOCKED) {
342                 mm->locked_vm += new_len >> PAGE_SHIFT;
343                 *locked = true;
344         }
345 
346         return new_addr;
347 }
348 
349 static struct vm_area_struct *vma_to_resize(unsigned long addr,
350         unsigned long old_len, unsigned long new_len, unsigned long *p)
351 {
352         struct mm_struct *mm = current->mm;
353         struct vm_area_struct *vma = find_vma(mm, addr);
354         unsigned long pgoff;
355 
356         if (!vma || vma->vm_start > addr)
357                 return ERR_PTR(-EFAULT);
358 
359         if (is_vm_hugetlb_page(vma))
360                 return ERR_PTR(-EINVAL);
361 
362         /* We can't remap across vm area boundaries */
363         if (old_len > vma->vm_end - addr)
364                 return ERR_PTR(-EFAULT);
365 
366         if (new_len == old_len)
367                 return vma;
368 
369         /* Need to be careful about a growing mapping */
370         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
371         pgoff += vma->vm_pgoff;
372         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
373                 return ERR_PTR(-EINVAL);
374 
375         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
376                 return ERR_PTR(-EFAULT);
377 
378         if (vma->vm_flags & VM_LOCKED) {
379                 unsigned long locked, lock_limit;
380                 locked = mm->locked_vm << PAGE_SHIFT;
381                 lock_limit = rlimit(RLIMIT_MEMLOCK);
382                 locked += new_len - old_len;
383                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
384                         return ERR_PTR(-EAGAIN);
385         }
386 
387         if (!may_expand_vm(mm, vma->vm_flags,
388                                 (new_len - old_len) >> PAGE_SHIFT))
389                 return ERR_PTR(-ENOMEM);
390 
391         if (vma->vm_flags & VM_ACCOUNT) {
392                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
393                 if (security_vm_enough_memory_mm(mm, charged))
394                         return ERR_PTR(-ENOMEM);
395                 *p = charged;
396         }
397 
398         return vma;
399 }
400 
401 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
402                 unsigned long new_addr, unsigned long new_len, bool *locked)
403 {
404         struct mm_struct *mm = current->mm;
405         struct vm_area_struct *vma;
406         unsigned long ret = -EINVAL;
407         unsigned long charged = 0;
408         unsigned long map_flags;
409 
410         if (offset_in_page(new_addr))
411                 goto out;
412 
413         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
414                 goto out;
415 
416         /* Ensure the old/new locations do not overlap */
417         if (addr + old_len > new_addr && new_addr + new_len > addr)
418                 goto out;
419 
420         ret = do_munmap(mm, new_addr, new_len);
421         if (ret)
422                 goto out;
423 
424         if (old_len >= new_len) {
425                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
426                 if (ret && old_len != new_len)
427                         goto out;
428                 old_len = new_len;
429         }
430 
431         vma = vma_to_resize(addr, old_len, new_len, &charged);
432         if (IS_ERR(vma)) {
433                 ret = PTR_ERR(vma);
434                 goto out;
435         }
436 
437         map_flags = MAP_FIXED;
438         if (vma->vm_flags & VM_MAYSHARE)
439                 map_flags |= MAP_SHARED;
440 
441         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
442                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
443                                 map_flags);
444         if (offset_in_page(ret))
445                 goto out1;
446 
447         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
448         if (!(offset_in_page(ret)))
449                 goto out;
450 out1:
451         vm_unacct_memory(charged);
452 
453 out:
454         return ret;
455 }
456 
457 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
458 {
459         unsigned long end = vma->vm_end + delta;
460         if (end < vma->vm_end) /* overflow */
461                 return 0;
462         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
463                 return 0;
464         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
465                               0, MAP_FIXED) & ~PAGE_MASK)
466                 return 0;
467         return 1;
468 }
469 
470 /*
471  * Expand (or shrink) an existing mapping, potentially moving it at the
472  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
473  *
474  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
475  * This option implies MREMAP_MAYMOVE.
476  */
477 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
478                 unsigned long, new_len, unsigned long, flags,
479                 unsigned long, new_addr)
480 {
481         struct mm_struct *mm = current->mm;
482         struct vm_area_struct *vma;
483         unsigned long ret = -EINVAL;
484         unsigned long charged = 0;
485         bool locked = false;
486 
487         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
488                 return ret;
489 
490         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
491                 return ret;
492 
493         if (offset_in_page(addr))
494                 return ret;
495 
496         old_len = PAGE_ALIGN(old_len);
497         new_len = PAGE_ALIGN(new_len);
498 
499         /*
500          * We allow a zero old-len as a special case
501          * for DOS-emu "duplicate shm area" thing. But
502          * a zero new-len is nonsensical.
503          */
504         if (!new_len)
505                 return ret;
506 
507         down_write(&current->mm->mmap_sem);
508 
509         if (flags & MREMAP_FIXED) {
510                 ret = mremap_to(addr, old_len, new_addr, new_len,
511                                 &locked);
512                 goto out;
513         }
514 
515         /*
516          * Always allow a shrinking remap: that just unmaps
517          * the unnecessary pages..
518          * do_munmap does all the needed commit accounting
519          */
520         if (old_len >= new_len) {
521                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
522                 if (ret && old_len != new_len)
523                         goto out;
524                 ret = addr;
525                 goto out;
526         }
527 
528         /*
529          * Ok, we need to grow..
530          */
531         vma = vma_to_resize(addr, old_len, new_len, &charged);
532         if (IS_ERR(vma)) {
533                 ret = PTR_ERR(vma);
534                 goto out;
535         }
536 
537         /* old_len exactly to the end of the area..
538          */
539         if (old_len == vma->vm_end - addr) {
540                 /* can we just expand the current mapping? */
541                 if (vma_expandable(vma, new_len - old_len)) {
542                         int pages = (new_len - old_len) >> PAGE_SHIFT;
543 
544                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
545                                        vma->vm_pgoff, NULL)) {
546                                 ret = -ENOMEM;
547                                 goto out;
548                         }
549 
550                         vm_stat_account(mm, vma->vm_flags, pages);
551                         if (vma->vm_flags & VM_LOCKED) {
552                                 mm->locked_vm += pages;
553                                 locked = true;
554                                 new_addr = addr;
555                         }
556                         ret = addr;
557                         goto out;
558                 }
559         }
560 
561         /*
562          * We weren't able to just expand or shrink the area,
563          * we need to create a new one and move it..
564          */
565         ret = -ENOMEM;
566         if (flags & MREMAP_MAYMOVE) {
567                 unsigned long map_flags = 0;
568                 if (vma->vm_flags & VM_MAYSHARE)
569                         map_flags |= MAP_SHARED;
570 
571                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
572                                         vma->vm_pgoff +
573                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
574                                         map_flags);
575                 if (offset_in_page(new_addr)) {
576                         ret = new_addr;
577                         goto out;
578                 }
579 
580                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
581         }
582 out:
583         if (offset_in_page(ret)) {
584                 vm_unacct_memory(charged);
585                 locked = 0;
586         }
587         up_write(&current->mm->mmap_sem);
588         if (locked && new_len > old_len)
589                 mm_populate(new_addr + old_len, new_len - old_len);
590         return ret;
591 }
592 

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